1. Field of Invention
The present invention relates to heating apparatus and more particularly to domestic heating apparatus utilizing apparatus for thermally circulating a liquid as disclosed in my prior U.S. Pat. No. 3,951,204.
2. Description of Prior Art
Due to rising energy costs various types of heating apparatus have been proposed to supplement or to replace conventional domestic heating systems and apparatus. Systems utilizing solar heat collectors and fireplace heat collectors, for example, are commercially available to supplement or replace conventional gas or electric heating systems. A major disadvantage of such apparatus is that in order to effectively transfer heat from the collection point to a storage point or to the area to be heated, considerable energy must be expended in transporting heat from an elevated position to a lower position where the heat is used or can be more easily distributed. The well known thermal syphon effect will operated to transfer heat from a lower position to a more elevated position, but since the reverse does not generally occur, mechanical apparatus such as pumps or blowers are generally utilized for transferring heat from a higher to a lower position. Solar collectors for instance, are usually roof mounted and pumps and blowers are conventionally utilized to transfer the collected heat from the roof level to a lower level where it is used or stored. Fireplace heat collectors must also utilize pumps or blowers for moving a heat transfer fluid to other areas in the building.
The use of pumps and blowers in systems of this type not only expends considerable energy but also requires expensive equipment and controls. Another disadvantage of such prior art systems is that additional controls are often required to prevent thermal flow from lower level heat sources such as boilers or furnaces, or heat storage tanks, to the upper level collectors which act as heat sinks when not in use. For example, in solar heating systems that utilize heat storage tanks or supplemental furnaces, if the collectors are roof mounted and are not separated from the lower level heat storage tanks or supplemental furnaces by valves or other means, during the night, energy can be lost through thermal flow to the collectors. Many collector systems ignore this "reverse energy flow" problem entirely and consequently considerable energy is wasted.